1. Field of the Invention
The present invention relates generally to the evaluation of light through an optical head, and more particularly to the evaluation of light in sub assembly testing of a multi-head optical storage system.
2. Background
Read-write optical heads that include active optics may be characterized by verification testing of an optical path of light that is altered by the optics. This testing may include a determination of the magnitude of a vector angle or a frequency response obtained based on the characterization of the optics.
Problems may result when evaluating the light during sub-assembly testing of read-write optical heads in a multi-head disk storage system, for example, when placing a light sensitive detector for monitoring the light between each of a plurality of flying heads comprising the subassembly. In this type of system, only one detector typically fits between the heads, requiring one fixture for up facing heads and a separate fixture for down facing heads. This approach also requires external circuitry to acquire a signal from separate detectors, preventing the use of a standard drive controller board to perform the test process. These detectors and fixturing add additional process steps to the assembly of the storage system, resulting in increased cost and handling of parts as well as potential damage to components. In this approach, there also does not exist any provision for measuring light in the return leg of the light and, thus, the complete optical path cannot be evaluated.
What is needed, therefore, is an improved method and apparatus for evaluating optical components in sub-assembly testing of multiple heads of a multi-disk optical system.
The present invention includes an apparatus for testing a head stack assembly, comprising: a substrate, wherein the substrate receives a light from the head stack assembly and directs a reflection of the light back to the head stack assembly, and wherein the head stack assembly is characterized based on the reflection of the light. The substrate may comprise a first surface, wherein first surface comprises a plurality of features for disrupting the reflection of the light. The substrate may further comprise a second surface disposed in generally parallel opposition to the first surface, wherein second surface comprises a plurality of features for disrupting the reflection of the light. The head stack assembly may comprise at least two optical heads, wherein the substrate comprises a surface, wherein the surface is disposed between the at least two optical heads, wherein the light from the head stack assembly received by the surface is delivered from a one of the at least two optical heads, and wherein the one of the at least two optical heads is characterized based on the reflection of the light from the surface. The light from the head stack assembly may be directed to the surface by a moveable part disposed on the optical head, wherein the moveable part acts to direct the light across the plurality of features. The present invention may further comprise and analyzer for analyzing the reflection of the light. The moveable part may comprise a steerable mirror, wherein the characterization comprises measurement of a voltage applied to the steerable mirror to deflect the steerable mirror. The head stack may comprise a plurality of optical fibers, wherein the characterization may be based on measurement of the reflection of the light from a particular one of the plurality of optical fibers. The characterization may also comprise an identification of a particular one of the plurality of optical fibers.
The present invention may also comprise a substrate, wherein the substrate receives light from the moveable optics; reflection means for providing a reflection of the light; and analyzing means for characterizing the moveable optics based on the reflection of the light. The reflection means may comprise disruption means for disrupting the light from the moveable optics. The moveable optics may comprise a steerable mirror.
The present invention may also comprise a method of testing a head stack assembly comprising the steps of: directing a light with optics of the head stack assembly toward a substrate, receiving a reflection of the light form the substrate, and characterizing the head stack assembly based on the reflection of the light. The present invention may further comprise a step of disrupting the light with substrate features. The present invention may further comprise a step of wherein the step of directing the light with the optics toward the substrate comprises directing the light with dynamic optics. The dynamic optics may comprise steerable optics. The present invention may further comprise a step of wherein the step of directing the light and receiving the reflection of the light comprises directing the light and receiving the reflection of the light with optics comprising an optical fiber. The present invention may further comprise a step of wherein the characterization includes detection of the reflected light from the optical fiber. The present invention may further comprise a step of wherein the characterization includes evaluating a functionality of the steerable optics. The present invention may further comprise a step of wherein the characterization includes evaluating a frequency response of the steerable optics.
Accordingly, several objects and advantages of the present invention are:
(a) to provide for the use of a computer to take, transfer, and store test results for head stack assemblies for later retrieval and analysis;
(b) to provide a means of testing a complete light path of an optical head-stack subassembly;
(c) to provide a means of testing micro-machined components;
(d) to provide a means of testing rotatable micro-machined mirrors for proper movement when a voltage is applied;
(e) to provide a measurement of the natural frequency of a micro-machined mirror;
(f) to provide a means of determining which optical fiber in a fiber bundle is attached to which flying optical head;
(g) to provide a means of determining which optical fiber attached to an optical head is located in an optical switch; and
(h) to accomplish the aforementioned testing using a single fixture and single installation of an optical head-stack sub-assembly.
The present invention may also comprise a data storage and retrieval system including a set of flying optical heads that are adapted for use with a set of spinning disks. The set of flying optical heads are coupled to a rotary actuator magnet and coil assembly by a respective suspension and actuator arm for positioning the set of heads over the surfaces of the set of spinning disks. In operation, lift forces are generated by aerodynamic interactions between the set of heads and the spinning disks. A flying height of a head (above the disk surface) is a balance of the lift force opposed by an equal and opposite spring force applied by each suspension. The optics of a given head are designed to be focused at a distance equal to said flying height.
In the present invention, a force measuring device known as a gram-load fixture may be modified to comprise an additional fixture providing a number of adapter plates preferably equaling one half the number of flying optical heads. These adapter plates are stacked such that they simulate disks of a drive assembly. A gram-load fixture is a device used to measure spring load force on each head of a head sub-assembly of a standard hard drive. As those skilled in the are aware, the gram-load measuring device individually determines the spring force acting on each head of the head sub-assembly. In this invention the adapter plates are included with the gram-load fixture to provide testing optics on the head.
The adapter plates provide a features from which a return beam of light is evaluated. The features can be made on any suitable substrate, the fixture design being such as to provide dimensions that approximate a typical flying head gap over a read-write surface while in operation. The evaluation may include determination of a vector angle and/or a mirror frequency response, provided the optics components on the head exhibit a dynamic component. In one embodiment of the invention, the dynamic component is provided by a moveable mirror, and features on the reflective surface contribute to evaluating head performance. Thus, in addition to measuring spring load force of the subassembly, optics components on the head can also be evaluated with one apparatus. In addition, bundled optical fibers coupled to the heads can be characterized by a determination as to which optical head is attached to which fiber.